This invention relates to speed enhancement of photographic film and, more particularly, it concerns a method and apparatus by which the sensitivity of photographic film to scene light may be increased by exposure of the film to a camera-contained supplemental light source.
It is known that the effective speed of photographic films can be increased by exposing the film to a low level, non-image forming light source either during fabrication of the film, during exposure of the film to image-forming light, as in a camera, or following removal from the camera. Exemplary disclosures of these techniques are found in U.S. Pat. No. 3,819,376, issued June 25, 1974 to Edwin H. Land (during film fabrication); U.S. Pat. Nos. 3,484,165, issued Dec. 16, 1969 to J. R. Denner, No. 3,577, 898, issued May 11, 1971 to Herbert E. Bragg, No. 3,823,413, issued July 9, 1974 to Melrose R. Cole, and No. 3,827,071, issued July 30, 1974 to G. L. Turpin (during film exposure in a camera); and U.S. Pat. No. 3,455,633, issued July 15, 1969 to Edwin H. Land (during the development or processing of exposed film). Of these basic approaches, the subjection of photographic film to a supplementary, uniform light source at about the time it is exposed to imaging light is advantageous in that any effects of aging on the enhanced film sensitivity are eliminated and, further, it offers a potential for correlating the supplementary, speed-enhancing light in accordance with scene light.
The prior art represented by the aforementioned Denner, Bragg, Turpin and Cole patents recognizes two approaches to the supplemental exposure of film in a camera. In the Denner and Bragg patents, a source of supplemental light external to the camera is used while in the Turpin and Cole patents internal camera light sources are used. In the latter arrangements, however, a problem is presented by the requirement that the camera area in front of the film transmit both image-forming light and the supplemental light. Thus, in order to achieve uniformity of non-image-forming supplemental light, an annular array of light sources is required.
In several issued U.S. patents which are assigned to the assignee in common with the assignee of the present invention, motion picture systems are disclosed in which exposure, processing and projection operations are carried out on a length of film contained at all times in a multipurpose cassette. The strip of film is initially wound on a supply spool within the cassette, and is advanced to a take-up spool when the cassette is placed in an appropriate camera for exposure in a conventional manner. After exposure, the cassette is placed into a projector apparatus which is capable of activating a cassette-contained processor to deposit a uniform coating layer of processing fluid along the length of the strip as it is rewound upon the supply spool. Thereafter, the apparatus projects the developed, recorded transparent images, and rewinds the film within the cassette for subsequent projection cycles.
The film used in such motion picture systems is exemplified by the disclosure of U.S. Pat. No. 3,848,871, issued July 15, 1975 to Edwin H. Land. The film is adapted to provide positive silver transfer images which may be viewed as a positive transparency without being separated from the developed negative image. Such films employ an additive color system in which light from the scene to be photographed passes a raster layer of color filters so that light-sensitive grains positioned behind the raster layer are exposed to different wave lengths of light corresponding to the color of the image photographed. On projection, the color is reproduced by the same raster layer in combination with the silver transferring images which, in themselves, are uncolored. While the film is particularly adapted for use in this system, it poses an additional problem to a camera-contained light source for enhancing the film speed.